The fastest American woman in the marathon will not toe the line in Los Angeles.

Deena Kastor announced today that an injury is preventing her from competing at the 2016 Olympic Marathon Trials. The American record-holder strained her left glute during a training session and informed fans on Twitter that "It's a strain I would have taken the risk to push through 8 yrs ago. Now, I'm more conservative."

Sidelined so late in the game. I'm out of the Trials but I'll see you in LA #LA2016 2 see who makes the Olympic team pic.twitter.com/8T8h2lETDs

— Deena Kastor (@DeenaKastor) February 10, 2016

. @FloTrack It's a strain I would have taken the risk to push through 8 yrs ago. Now, I'm more conservative.

— Deena Kastor (@DeenaKastor) February 10, 2016

Kastor, 42, ran 2:27:47 at the 2015 Chicago Marathon, her fastest performance since setting the American record of 2:19:36 in London in 2006. The three-time Olympian had the fourth-fastest time heading into Saturday's race. But instead will be on the streets cheering for her Mammoth Track Club teammates.



With Kastor out, that makes four Olympians, Ryan Hall, Matt Tegenkamp and Abdi Abdirahman, who have recently withdrawn from the race or retired before the 2016 Olympic Marathon Trials. 

READ: RYAN VAIL HAS DROPPED OUT OF THE OLYMPIC MARATHON TRIALS

The Olympic Trials Marathon will be live on NBC.